U.S. patent number 8,502,930 [Application Number 12/956,122] was granted by the patent office on 2013-08-06 for electrically-driven liquid crystal lens and stereoscopic display device using the same.
This patent grant is currently assigned to LG Display Co., Ltd.. The grantee listed for this patent is Hee Jin Im. Invention is credited to Hee Jin Im.
United States Patent |
8,502,930 |
Im |
August 6, 2013 |
Electrically-driven liquid crystal lens and stereoscopic display
device using the same
Abstract
Disclosed are an electrically-driven liquid crystal lens which
includes a light shade to be switched on/off according to whether
or not voltage is applied, reducing a cell gap of a liquid crystal
layer, and a stereoscopic display device using the same, the
electrically-driven liquid crystal lens includes first and second
substrates opposite each other and each including plural lens
regions and a light shade provided at a boundary of each lens
region, first electrodes formed in a given direction on the first
substrate in each lens region, a second electrode formed on the
second substrate and having an aperture corresponding to the light
shade, first and second light shade switching electrodes formed at
the light shade and extending parallel to the first electrodes, a
liquid crystal layer between both the substrates, and a polarizer
plate formed above the second substrate and having a first
transmission axis.
Inventors: |
Im; Hee Jin (Gyeonggi-do,
KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
Im; Hee Jin |
Gyeonggi-do |
N/A |
KR |
|
|
Assignee: |
LG Display Co., Ltd. (Seoul,
KR)
|
Family
ID: |
44187121 |
Appl.
No.: |
12/956,122 |
Filed: |
November 30, 2010 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20110157496 A1 |
Jun 30, 2011 |
|
Foreign Application Priority Data
|
|
|
|
|
Dec 30, 2009 [KR] |
|
|
10-2009-0134354 |
|
Current U.S.
Class: |
349/15; 349/200;
349/74 |
Current CPC
Class: |
H04N
13/356 (20180501); H04N 13/322 (20180501); H04N
13/305 (20180501); G02B 30/27 (20200101); H04N
2213/001 (20130101) |
Current International
Class: |
G02F
1/1335 (20060101); G02F 1/1347 (20060101); G02F
1/13 (20060101) |
Field of
Search: |
;349/15,74,200 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Merlin; Jessica M
Attorney, Agent or Firm: Morgan, Lewis & Bockius LLP
Claims
What is claimed is:
1. An electrically-driven liquid crystal lens comprising: a first
substrate and a second substrate arranged opposite each other and
each including a plurality of lens regions and a light shade
provided at a boundary of each lens region; a plurality of first
electrodes formed in a given direction on the first substrate in
each lens region; a second electrode formed on one surface of the
second substrate and having an aperture corresponding to the light
shade; first and second light shade switching electrodes formed at
opposite ends of the light shade and extending parallel to the
first electrodes; a liquid crystal layer filled between the first
substrate and the second substrate; a first voltage source to
create a vertical electric field between the plurality of first
electrodes and the second electrode; a second voltage source to
create a horizontal electric filed between the first and second
light shade switching electrodes; and a polarizer plate formed on
the other surface of the second substrate and having a first
transmission axis, wherein liquid crystals in the light shade are
aligned to follow a direction crossing the first transmission axis
when the second voltage source applies different voltages to the
first and second light shade switching electrodes.
2. The lens according to claim 1, wherein the first voltage source
applies voltages, which gradually increase from a center to the
boundary of the lens region, to the first electrodes.
3. The lens according to claim 1, wherein a 2-dimensional (2D)
image signal is transmitted along the first transmission axis from
a display panel below the first substrate.
4. The lens according to claim 1, wherein the plurality of first
electrodes is formed in the same layer on the first substrate.
5. The lens according to claim 1, further comprising at least one
insulating film on the first substrate, wherein the plurality of
first electrodes is divided onto the first substrate and the
insulating film, and the first electrodes on the first substrate
and the first electrodes on the insulating film are arranged at
alternating positions.
6. A stereoscopic display device comprising: an electrically-driven
liquid crystal lens including a first substrate and a second
substrate arranged opposite each other and each including a
plurality of lens regions and a light shade provided at a boundary
of each lens region, a plurality of first electrodes formed in a
given direction on the first substrate in each lens region, a
second electrode formed on one surface of the second substrate and
having an aperture corresponding to the light shade, first and
second light shade switching electrodes formed at opposite ends of
the light shade and extending parallel to the first electrodes, and
a liquid crystal layer filled between the first substrate and the
second substrate; a display panel located below the
electrically-driven liquid crystal lens to transmit a 2-dimensional
(2D) image signal; a first polarizer plate located between the
display panel and the electrically-driven liquid crystal lens and
having a first transmission axis; a second polarizer plate located
on the electrically-driven liquid crystal lens and having the same
transmission axis as the first transmission axis; a first voltage
source to create a vertical electric field between the plurality of
first electrodes and the second electrode on a per lens region
basis; and a second voltage source to create a horizontal electric
filed between the first and second light shade switching electrodes
wherein liquid crystals in the light shade are aligned to follow a
direction crossing the first transmission axis when the second
voltage source applies different voltages to the first and second
light shade switching electrodes.
7. The device according to claim 6, wherein: the first and second
voltage sources are switched off to perform display of a 2D image;
and the first and second voltage sources are switched on to perform
display of a 3-dimensional (3D) image.
8. The device according to claim 6, wherein the plurality of first
electrodes and the second electrode are made of transparent
electrodes.
Description
This application claims the benefit of the Korean Patent
Application No. 10-2009-0134354, filed on Dec. 30, 2009, which is
hereby incorporated by reference as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrically-driven liquid
crystal lens, and more particularly, to an electrically-driven
liquid crystal lens which includes a light shade to be switched on
or off according to whether or not voltage is applied thereto,
thereby reducing a cell gap of a liquid crystal layer, and a
stereoscopic display device using the same.
2. Discussion of the Related Art
At present, services for rapid dissemination of information, to be
constructed based on high-speed information communication networks,
have developed from a simple "listening and speaking" service, such
as current telephones, to a "watching and listening" multimedia
type service based on digital terminals used for high-speed
processing of characters, voices and images, and are expected to be
ultimately developed into hyperspace 3-dimensional stereoscopic
information communication services enabling virtual reality and
stereoscopic viewing free from the restrains of time and space.
In general, stereoscopic images representing 3-dimensions are
realized based on the principle of stereo-vision via the viewer's
eyes. However, since the viewer's eyes are spaced apart from each
other by about 65 mm, i.e. have a binocular parallax, the left and
right eyes perceive slightly different images due to a positional
difference between the two eyes. Such an image difference due to
the positional difference between the two eyes is called binocular
disparity. A 3-dimensional stereoscopic image display device is
designed based on binocular disparity, allowing the left eye to
view only an image for the left eye and the right eye to view only
an image for the right eye.
Specifically, the left and right eyes view different 2-dimensional
images, respectively. If the two different images are transmitted
to the brain through the retina, the brain accurately combines the
images, reproducing depth perception and realism of an original
3-dimensional (3D) image. This ability is conventionally referred
to as stereography (stereoscopy), and a display device to which
stereoscopy is applied is referred to as a stereoscopic display
device.
In the meantime, stereoscopic display devices may be classified
based on constituent elements of a lens which realizes
3-dimensional images. In one example, a lens using a liquid crystal
layer is referred to as an electrically-driven liquid crystal
lens.
Generally, a liquid crystal display device includes two electrodes
opposite each other, and a liquid crystal layer interposed between
the two electrodes. Liquid crystal molecules of the liquid crystal
layer are driven by an electric field created when voltages are
applied to the two electrodes. The liquid crystal molecules have
polarization and optical anisotropy characteristics. Here,
polarization refers to a change in molecular arrangement direction
according an electric field, which is caused as electrons in liquid
crystal molecules are gathered to opposite sides of the liquid
crystal molecules when the liquid crystal molecules are under the
influence of an electric field. Also, optical anisotropy refers to
a change in path or polarization of light to be emitted according
to an incidence direction or polarization of incident light, which
is caused by an elongated shape of liquid crystal molecules and the
above-mentioned molecular arrangement direction.
Accordingly, the liquid crystal layer has a transmittance
difference due to voltages applied to the two electrodes, and is
able to display an image by varying the transmittance difference on
a per pixel basis.
Recently, there has been proposed an electrically-driven liquid
crystal lens in which a liquid crystal layer serves as a lens based
on the above-described characteristics of liquid crystal
molecules.
Specifically, a lens is designed to control a path of incident
light on a per position basis using a difference between a
refractive index of a lens constituent material and a refractive
index of air. In the electrically-driven liquid crystal lens, if
different voltages are applied to electrodes located at different
positions of the liquid crystal layer so as to create an electric
field required to drive the liquid crystal layer, incident light
introduced into the liquid crystal layer undergoes different phase
variations on a per position basis, and as a result, the liquid
crystal layer is able to control the path of the incident light in
the same manner as an actual lens.
Hereinafter, an electrically-driven liquid crystal lens of related
art will be described with reference to the accompanying
drawings.
FIG. 1 is a sectional view illustrating an electrically-driven
liquid crystal lens of the related art, and FIG. 2 is a schematic
view illustrating a potential distribution of the
electrically-driven liquid crystal lens of FIG. 1 after voltage is
applied to the electrically-driven liquid crystal lens.
As illustrated in FIG. 1, the electrically-driven liquid crystal
lens includes first and second substrates 10 and 20 opposite each
other, and a liquid crystal layer 30 formed between the first
substrate 10 and the second substrate 20.
First electrodes 11 are arranged on the first substrate 10 and are
spaced apart from one another by a first distance. In the two
neighboring first electrodes 11, a distance from the center of one
first electrode 11 to the center of the other first electrode 11 is
referred to as a "pitch". Repeating the same pitch for the
respective first electrodes results in a pattern.
A second electrode 21 is formed over the entire surface of the
second substrate 20 opposite the first substrate 10.
The first and second electrodes 11 and 21 are made of transparent
metal. The liquid crystal layer 30 is formed in a space between the
first electrodes 11 and the second electrode 21. Liquid crystal
molecules of the liquid crystal layer 30 have a parabolic potential
surface due to a property reacting according to the intensity and
distribution of an electric field and thus, have a phase
distribution similar to that of the electrically-driven liquid
crystal lens as illustrated in FIG. 2.
The above-described electrically-driven liquid crystal lens is
realized under the condition that high voltages are applied to the
first electrode 11 and the second electrode 21 is grounded. With
this voltage condition, a vertical electric field is strongest at
the center of the first electrode 11, and the intensity of the
vertical electric field decreases away from the first electrode 11.
Accordingly, if the liquid crystal molecules of the liquid crystal
layer 30 have positive dielectric anisotropy, the liquid crystal
molecules are arranged according to the electric field in such a
way that the liquid crystal molecules are upright at the center of
the first electrode 11 and are gradually tilted approximately
horizontally away from the first electrode 11. As a result, in view
of light transmission, an optical path is shortened at the center
of the first electrode 11, and is lengthened with increasing
distance from the first electrode 11, as illustrated in FIG. 2.
Representing the length variation of the optical path using a phase
surface, the electrically-driven liquid crystal lens has light
transmission effects similar to a lens having a parabolic
surface.
Here, the second electrode 21 causes behavior of the electric field
created by the liquid crystal molecules, making a refractive index
of light spatially take the form of a parabolic function. The first
electrode 11 corresponds to a lens edge region.
In this case, relatively high voltages are applied to the first
electrodes 11 than the second electrode 21. Therefore, as
illustrated in FIG. 2, an electric potential difference occurs
between the first electrodes 11 and the second electrode 21. In
particular, a steep lateral electric field is created around the
first electrodes 11. Accordingly, liquid crystals have a slightly
distorted distribution rather than a gentle distribution, whereby a
refractive index of light cannot exhibit parabolic spatial
distribution, or movement of the liquid crystals is excessively
sensitive to voltage variation.
The above-described electrically-driven liquid crystal lens of the
related art may be realized, without a lens having a parabolic
surface, by arranging electrodes on two substrates with liquid
crystals interposed therebetween and applying voltages to the
electrodes.
The above described electrically-driven liquid crystal lens has the
following problems.
Firstly, since the electrodes formed on the lower substrate are
positioned at only a part of a lens region, a steep lateral
electric field, rather than a gentle electric field, is created
between a lens edge region corresponding to the electrode and a
lens center region distant from the lens edge region, resulting in
a slightly distorted phase of the electrically-driven liquid
crystal lens. In particular, in the electrically-driven liquid
crystal lens that is driven by a liquid crystal field, since the
greater the pitch of lens regions, the smaller the number of
electrodes to which high voltages are applied, an insufficient
electric field is created between the high voltage electrodes and a
substrate opposite these electrodes. Accordingly, it becomes
difficult to form the electrically-driven liquid crystal lens
having a gentle parabolic lens surface, which has the same effects
as an actual lens.
Secondly, when being applied to a large-area display device, the
lens center region, which is distant from the lens edge region
where the electrode, to which high-voltage is applied, is located,
is substantially unaffected by an electric field and has a
difficulty in alignment control of liquid crystals by the electric
field. As occasion demands, if the alignment control in the lens
center region is difficult or impossible, the resulting
electrically-driven liquid crystal lens has a discontinuous lens
profile and is ineffective as a lens.
Thirdly, since a vertical electric field, created between an
electrode to which a high voltage is applied and an electrode
formed over the entire surface of a substrate opposite the high
voltage electrode, causes a high height, i.e. high sag of the
electrically-driven liquid crystal lens and also, the
electrically-driven liquid crystal lens requires upper and lower
sag margins, a great quantity of liquid crystals may be required to
form the entire electrically-driven liquid crystal lens. In
particular, since the greater the sag of the electrically-driven
liquid crystal lens, the greater the quantity of liquid crystals on
a per volume basis, this may result in cost increase and serious
deterioration in process efficiency.
Fourthly, a focal distance of the electrically-driven liquid
crystal lens is inversely proportional to the sag of the
electrically-driven liquid crystal lens. To fabricate an
electrically-driven liquid crystal lens having a short focal
distance, there is a need for a liquid crystal layer having a large
thickness and this becomes a main factor of cost increase. In
particular, since the quantity of very expensive liquid crystals
increases on a per volume basis as a cell gap increases, there is
increasing a demand to reduce the cell gap.
In the electrically-driven liquid crystal lens of the related art,
to assure a constant lens profile, the thickness of the liquid
crystal layer, i.e. the cell gap must be 30 .mu.m or more and in
particular, in the case of a large-area one having a large pitch,
the thickness of the liquid crystal layer is further increased.
However, an array process for a display panel, such as a liquid
crystal panel, forms a cell gap of 10 .mu.m or less, and therefore,
is difficult to form the above described high large cell gap of the
liquid crystal layer. That is, a current array process forming a
liquid crystal panel is difficult to form the liquid crystal layer
of the above described electrically-driven liquid crystal lens.
Fifthly, although a Fresnel lens has been proposed in an effort to
reduce the above described cell gap, the Fresnel lens has
discontinuous surfaces between the respective neighboring sub
regions of each lens region having different maximum height points,
and thus, causes deterioration in display grade.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an
electrically-driven liquid crystal lens and a stereoscopic display
device using the same that substantially obviate one or more
problems due to limitations and disadvantages of the related
art.
An object of the present invention is to provide an
electrically-driven liquid crystal lens which includes a light
shade to be switched on or off according to whether or not voltage
is applied thereto, thereby reducing a cell gap of a liquid crystal
layer, and a stereoscopic display device using the same.
Additional advantages, objects, and features of the invention will
be set forth in part in the description which follows and in part
will become apparent to those having ordinary skill in the art upon
examination of the following or may be learned from practice of the
invention. The objectives and other advantages of the invention may
be realized and attained by the structure particularly pointed out
in the written description and claims hereof as well as the
appended drawings.
To achieve these objects and other advantages and in accordance
with the purpose of the invention, as embodied and broadly
described herein, an electrically-driven liquid crystal lens
includes a first substrate and a second substrate arranged opposite
each other and each including a plurality of lens regions and a
light shade provided at a boundary of each lens region, a plurality
of first electrodes formed in a given direction on the first
substrate in each lens region, a second electrode formed on one
surface of the second substrate and having an aperture
corresponding to the light shade, first and second light shade
switching electrodes formed at opposite ends of the light shade and
extending parallel to the first electrodes, a liquid crystal layer
filled between the first substrate and the second substrate, and a
polarizer plate formed on the other surface of the second substrate
and having a first transmission axis.
The electrically-driven liquid crystal lens may further include a
first voltage source to create a vertical electric field between
the plurality of first electrodes and the second electrode, and a
second voltage source to create a horizontal electric filed between
the first and second light shade switching electrodes.
The first voltage source may apply voltages, which gradually
increase from a center to the boundary of the lens region, to the
first electrodes.
Liquid crystals in the light shade may be aligned to follow a
direction crossing the first transmission axis when the second
voltage source applies different voltages to the first and second
light shade switching electrodes. In this case, a 2-dimensional
(2D) image signal may be transmitted along the first transmission
axis from a display panel below the first substrate.
The plurality of first electrodes may be formed in the same layer
on the first substrate. The electrically-driven liquid crystal lens
may further include at least one insulating film on the first
substrate, and the plurality of first electrodes may be divided
onto the first substrate and the insulating film, and the first
electrodes on the first substrate and the first electrodes on the
insulating film may be arranged at alternating positions.
In accordance with another aspect of the present invention, a
stereoscopic display device includes an electrically-driven liquid
crystal lens including a first substrate and a second substrate
arranged opposite each other and each including a plurality of lens
regions and a light shade provided at a boundary of each lens
region, a plurality of first electrodes formed in a given direction
on the first substrate in each lens region, a second electrode
formed on one surface of the second substrate and having an
aperture corresponding to the light shade, first and second light
shade switching electrodes formed at opposite ends of the light
shade and extending parallel to the first electrodes, and a liquid
crystal layer filled between the first substrate and the second
substrate, a display panel located below the electrically-driven
liquid crystal lens to transmit a 2-dimensional (2D) image signal,
a first polarizer plate located between the display panel and the
electrically-driven liquid crystal lens and having a first
transmission axis, a second polarizer plate located on the
electrically-driven liquid crystal lens and having the same
transmission axis as the first transmission axis, a first voltage
source to create a vertical electric field between the plurality of
first electrodes and the second electrode on a per lens region
basis, and a second voltage source to create a horizontal electric
filed between the first and second light shade switching
electrodes.
The first and second voltage sources may be switched off to perform
display of a 2D image, and the first and second voltage sources may
be switched on to perform display of a 3-dimensional (3D)
image.
The plurality of first electrodes and the second electrode may be
made of transparent electrodes.
It is to be understood that both the foregoing general description
and the following detailed description of the present invention are
exemplary and explanatory and are intended to provide further
explanation of the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are included to provide a further
understanding of the invention and are incorporated in and
constitute a part of this application, illustrate embodiment(s) of
the invention and together with the description serve to explain
the principle of the invention. In the drawings:
FIG. 1 is a sectional view illustrating an electrically-driven
liquid crystal lens of related art;
FIG. 2 is a view illustrating a potential distribution after a
voltage is applied to the electrically-driven liquid crystal lens
of FIG. 1;
FIG. 3 is a view comparing lens effects and cell gaps between the
electrically-driven liquid crystal lens according to the present
invention and a general electrically-driven liquid crystal
lens.
FIG. 4 is a perspective view of the electrically-driven liquid
crystal lens according to the present invention;
FIG. 5 is a plan view illustrating a configuration of electrodes on
a first substrate of the electrically-driven liquid crystal lens
according to the present invention;
FIG. 6 is a graph illustrating a relationship between the maximum
lens height and the width of a light shade provided in the
electrically-driven liquid crystal lens according to the present
invention; and
FIG. 7 is a sectional view illustrating a stereoscopic display
device according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Reference will now be made in detail to an electrically-driven
liquid crystal lens and a stereoscopic display device using the
same according to the preferred embodiments of the present
invention, examples of which are illustrated in the accompanying
drawings. Wherever possible, the same reference numbers will be
used throughout the drawings to refer to the same or like
parts.
FIG. 3 is a view comparing lens effects and cell gaps between the
electrically-driven liquid crystal lens according to the present
invention and a general electrically-driven liquid crystal
lens.
As illustrated in FIG. 3, the electrically-driven liquid crystal
lens of the present invention includes a light shade BM formed at a
boundary of a lens region. The light shade BM serves to reduce a
cell gap to half or less that of a general electrically-driven
liquid crystal lens.
When the light shade covers a boundary of a desired unit lens
region of the electrically-driven liquid crystal lens (here, the
boundary corresponds to a lens edge region where neighboring lens
regions meet), it is possible to reduce the thickness of a cell gap
by the same value as the width of the light shade.
It is noted that the light shade BM causes brightness deterioration
equal to the width covered by the light shade BM upon display of a
3-dimensional (3D) image (stereoscopic display). Therefore, it is
important to optimize a ratio of the width of the light shade BM to
a reduced cell gap thickness.
In the illustrated embodiment, only half a desired lens height of a
lens region is realized and the remaining lens region is covered by
the light shade. In this case, although light loss of about 27%
occurs, the resulting cell gap can be reduced to 50% of a general
cell gap thickness. However, it is also possible to reduce the cell
gap thickness to half or more the cell gap thickness of the related
art. The cell gap thickness and the width of the light shade are
set in consideration of brightness upon display of a 3D image.
In this case, the light shade may be switched on or off by an
electric field. Upon formation of a 2-dimensional (2D) image, the
light shade is switched off such that a 2D image signal transmitted
from a display panel below the light shade is directly emitted
through a corresponding light shade region and thus, there is no
brightness deterioration.
The width of the light shade may be changed according to a pitch
and a desired cell gap, and is set in consideration of brightness
required for display of a 3D image and a realizable cell gap
thickness.
FIG. 4 is a perspective view of the electrically-driven liquid
crystal lens according to the present invention, and FIG. 5 is a
plan view illustrating a configuration of electrodes on a first
substrate of the electrically-driven liquid crystal lens according
to the present invention.
As illustrated in FIG. 4, the electrically-driven liquid crystal
lens according to the present invention includes a plurality of
lens regions, and a light shade BM is defined at a boundary of each
lens region. As described above, the light shade BM is switched on
or off according to whether or not voltage is applied. When it is
desired to display a 2D image, the light shade BM is switched off
to directly emit a 2D image transmitted from a display panel
therebelow. That is, the light shade BM is a switchable black
matrix.
Considering the electrically-driven liquid crystal lens according
to the present invention in detail, the electrically-driven liquid
crystal lens includes a first substrate 110 and a second substrate
120 arranged opposite each other, a plurality of first electrodes
111 and 112 formed in a given direction on the first substrate 110
in each lens region, a second electrode 121 formed on the second
substrate 120 and having an aperture OP corresponding to the light
shade, first and second light shade switching electrodes 118a and
118b formed parallel to the first electrodes 111 and 112 at
opposite ends of the light shade, a liquid crystal layer 150 filled
between the first substrate 110 and the second substrate 120, and a
polarizer plate 160 formed on a surface of the second substrate 120
and having a transmission axis.
The electrically-driven liquid crystal lens further includes a
first voltage source VS1 to create a vertical electric field
between the plurality of first electrodes 111 and 112 and the
second electrode 121, and a second voltage source VS2 to create a
horizontal electric field between the first and second light shade
switching electrodes 118a and 118b. The electrically-driven liquid
crystal lens performs display of a 3D image upon receiving
corresponding voltages from these voltage sources VS1 and VS2. More
specifically, the first and second voltage sources VS1 and VS2
apply voltages to the first and second light shade switching
electrodes 118a and 118b, enabling display of a 3D image.
If no voltage is applied from the first and second voltage sources
VS1 and VS2 to the first electrodes 111 and 112, the second
electrode 121 and the light shade switching electrodes 118a and
118b, a 2D image emitted from a display panel located below the
electrically-driven liquid crystal lens is displayed.
As illustrated in FIG. 5, the first voltage source VS1 applies
voltages Vmax, . . . V1, which gradually increase from the center
to the boundary of the lens region, to the first electrodes 111 and
112. These voltage sources apply voltages to metal pads 63 provided
at one end of the respective first electrodes 111 and 112 extending
in the given direction. Here, the first electrodes 111 and 112 are
transparent electrodes and are connected at one end thereof to the
metal pads 63 via pad contact holes 71. The metal pads 63 are
located at an outer periphery of a display part of the
electrically-driven liquid crystal lens.
The first electrodes 111 and 112, as illustrated in FIG. 4, may be
formed in different layers on the first substrate 110 with an
insulating film 115 interposed therebetween, or may be formed in
the same layer. In addition, although the embodiment illustrates
that the first electrodes 111 and 112 are densely arranged with a
small distance therebetween, the first electrodes 111 and 112 may
be formed in the same layer if a distance therebetween is further
increased.
The second electrode 121 includes the aperture Op located at each
lens edge region, and the remaining region of the second electrode
121 except for the aperture OP has an integrally connected shape on
the second substrate 120.
The second voltage source VS2 applies different voltages to the
first and second light shade switching electrodes 118a and 118b,
thereby creating a horizontal electric field between the two
electrodes.
When the second voltage source VS2 applies different voltages to
the first and second light shade switching electrodes 118a and
118b, preferably, liquid crystals in the light shade are aligned to
follow a direction crossing the transmission axis of the polarizer
plate 160. Accordingly, liquid crystal molecules between the first
and second light shade switching electrodes 118a and 118b in the
light shade, which are driven by the horizontal electric field, are
aligned in a direction crossing the transmission axis of the
polarizer plate 160. This causes the light shade so as not to be
seen, allowing the light shade to function as a black matrix when
voltage is applied.
In this case, a 2D image signal is transmitted along the
transmission axis from a display panel (200, see FIG. 7) below the
first substrate 110. Here, a polarizer plate on the display panel
and the polarizer plate on the electrically-driven liquid crystal
lens have the same directional transmission axis, which crosses an
alignment direction of liquid crystals caused when voltage is
applied.
In addition, as illustrated in FIG. 5, the second voltage source
VS2 applies different voltage signals Vsp1 and Vsp2 to the first
and second light shade switching electrodes 118a and 118b at the
boundary of each lens region. To this end, the first and second
light shade switching electrodes 118a and 118b are connected to
metal pads 65 formed at one end or both ends thereof. The first and
second light shade switching electrodes 118a and 118b in the form
of transparent electrodes and the metal pads 65 are formed in
different layers and are connected to the metal pads 65 via pad
contact holes 70. In this case, the metal pads 65 are located at
the outer periphery of the display part of the electrically-driven
liquid crystal lens.
The light shade is formed between the two neighboring lens regions,
and the width of the light shade is the sum of half that of one
lens region and half that of the other lens region. Specifically, a
region, which is located at either end of the lens region L and is
designated by reference characters BM, has a width half the width
of the light shade.
When voltages are applied to the neighboring first electrodes 111
and 112, a voltage difference between the first electrodes is 1V or
less to prevent generation of a strong horizontal electric field
between the first electrodes 111 and 112.
The plurality of first electrodes 111 and 112 in the lens region L
is horizontally symmetrically formed on the basis of the edge of
the lens region.
Here, the lowest threshold voltage V1 applied to the first
electrode 111 or 112 corresponding to the center O of the lens
region L is an Alternating Current (AC) square wave voltage having
a peak value of about 1.4-2V. The threshold voltage V1 is
calculated by expression of
.pi..times..times..times..DELTA..times..times. ##EQU00001## (where,
.DELTA..epsilon. is the dielectric anisotropy of liquid crystals,
K1 is the modulus of elasticity of liquid crystals, and
.epsilon..sub.o is a free-space dielectric constant). In addition,
the highest voltage Vmax applied to the first electrodes 111 and
112 corresponding to the edge E of the lens region L is an AC
square wave voltage having a peak value of about 2.5.about.10V.
In this case, a ground voltage or a voltage smaller than a
threshold voltage is applied to the second electrode 121. In this
case, a pattern of the second electrode 121 corresponding to the
light shade is removed and thus, no vertical electric field is
created in the light shade.
Reference numerals 131 and 132 represent first and second alignment
films. To allow the electrically-driven liquid crystal lens to
function as a transparent layer in an initial state in which no
voltage is applied, a rubbing direction of the first alignment film
131 may be parallel to or perpendicular to a longitudinal direction
of the first electrodes 111 and 112. In this case, the second
alignment film 132 has a rubbing direction crossing or
anti-parallel to the rubbing direction of the first alignment film
131. Thereby, an image transmitted from the display panel below the
electrically-driven liquid crystal lens is directly transmitted to
the viewer.
The plurality of first electrodes 111 and 112 has a bar shape
extending in a given direction along a longitudinal direction of
the first substrate 110 or the insulating film 115 (i.e. a
direction of one side of the first substrate 110). The width of
each first electrode 111 or 112 is 1.about.10 .mu.m, and a distance
between the neighboring first electrodes 111 and 112 is 1.about.10
.mu.m. For example, the pitch is variously variable in a range of
90.about.1000 .mu.m. According to the above-described width and
distance of the first electrodes 111 and 112, approximately ten to
one hundred or more first electrodes can be formed on a per lens
region basis.
Although not shown, a seal pattern (not shown) is formed at outer
peripheral region of the first and second substrates 110 and 120
(i.e. a non-display region including a pad portion) to maintain a
gap between the first substrate 110 and the second substrate 120.
The liquid crystal layer 150 between the first substrate 110 and
the second substrate 120 may be reduced in thickness to 30 .mu.m or
less with provision of the light shade. To stably maintain the
thickness of the liquid crystal layer 150, ball spacers or column
spacers may be further provided to support the cell gap between the
first substrate 110 and the second substrate 120. In this case, it
is advantageous to position the spacers so as not to distort the
phase of the electrically-driven liquid crystal lens.
Although the first and second light shade switching electrodes 118a
and 118b may be formed of metal as occasion demands, the first and
second light shade switching electrodes 118a and 118b may be formed
in the same layer as the first electrodes 111 and 112 in the form
of transparent electrodes. This may result in an abbreviated
process sequence.
As the first electrodes 111 and 112 having the same width are
arranged on the first substrate 110 and voltages gradually
decreasing from the edge E to the center O of the lens region L are
applied to the first electrodes 111 and 112, a gentle vertical
electric field is generated between the first electrodes 111 and
112 and the second electrode 121 and a slight horizontal electric
field is generated between the neighboring first electrodes 111 and
112. Consequently, a gentle lateral electric field may be observed,
in which the intensity of the electric field is high at the edge E
of the lens region L and is low at the center O of the lens region
L.
Representing the length of an optical path of liquid crystals
aligned on a per position basis of an electric field, it can be
appreciated that the electrically-driven liquid crystal lens has a
shape similar to a gentle parabolic lens, in which the edge E of
the lens region L has the shortest optical path and the center O of
the lens region L has the longest optical path.
Here, the voltages applied to the first electrodes 111 and 112 and
the second electrode 121 causes behavior of the electric field
created by the liquid crystal molecules, making a refractive index
of light spatially take the form of a parabolic function.
The width and distance of the first electrodes 111 and 112 may have
equal values, or one of the width and distance may have an unequal
value, or both the width and the distance may have unequal values.
Changes in the width and distance of the first electrodes may
depend on a lens profile.
FIG. 6 is a graph illustrating a relationship between the maximum
lens height and the width of the light shade provided in the
electrically-driven liquid crystal lens according to the present
invention.
As illustrated in FIG. 6, considering a relationship between the
cell gap thickness and the width of the light shade BM, the width
of the light shade BM is proportional to the square of a reduced
cell gap thickness.
Since an ideal lens takes the form of a quadratic function, a lens
sag (i.e. a desired lens height) is reduced as much as the square
of the width of the light shade.
In addition, since the cell gap of the liquid crystal layer is
proportional to the lens sag, the smaller the lens sag, the smaller
the cell gap.
The cell gap of the related art corresponds to 110.about.130% of
the maximum lens height. Although a desired cell gap is slightly
changed according to an application model, the electrically-driven
liquid crystal lens of the present invention may achieve a reduced
cell gap equal to half or less that of the cell gap of the related
art owing to the above described switchable light shade.
The width of the light shade and the cell gap represent a trade-off
as described above, and may be set according to a corresponding
model.
FIG. 7 is a sectional view illustrating a stereoscopic display
device including the electrically-driven liquid crystal lens
according to the present invention.
As illustrated in FIG. 7, the stereoscopic display device of the
present invention includes the above described electrically-driven
liquid crystal lens 100, a display panel 200, which is disposed
below the electrically-driven liquid crystal lens 100 and serves to
transmit a 2D image signal, a first polarizer plate 210 located
between the display panel 200 and the electrically-driven liquid
crystal lens 100 and having a first transmission axis, a second
polarizer plate 160 located on the electrically-driven liquid
crystal lens 100 and having the same transmission axis as the first
transmission axis, the first voltage source VS1 to apply voltages,
which gradually increase from the center to the edge of the lens
region, to the first electrodes 111 and 112 in each lens region and
to apply a common voltage to the second electrode 121, and the
second voltage source VS2 to apply a voltage required to drive
liquid crystals in a direction crossing the first transmission axis
between the first and second light shade switching electrodes 118a
and 118b.
The first and second voltage sources VS1 and VS2 may be switched
off to enable display of a 2D image, or may be switched on to
enable display of a 3D image.
The display panel 200 may be selected from various flat-panel
displays including a Liquid Crystal Display (LCD), Organic Light
Emitting Display (OLED), Plasma Display Panel (PDP), Field Emission
Display (FED), etc. The display panel 200 is located below the
electrically-driven liquid crystal lens 100, and serves to transmit
a 2D image signal to the electrically-driven liquid crystal lens
100.
As apparent from the above description, an electrically-driven
liquid crystal lens and a stereoscopic display device using the
same according to the present invention have the following
effects.
Firstly, to assure a precise and stable profile of the
electrically-driven liquid crystal lens, a lower plate is provided
with first finely split electrodes and different voltages are
applied to the first electrodes, such that a vertical electric
filed is created between the first electrodes and a second
electrode formed on an upper plate, providing the
electrically-driven liquid crystal lens with a gentle parabolic
lens shape.
Secondly, as a light shade is provided to correspond to a boundary
of a lens region, it is possible to reduce a call gap. The boundary
of the lens region has a high crosstalk region and it is possible
to reduce the cell gap without significant brightness loss. In
particular, instead of causing crosstalk at each boundary between
neighboring ones of a plurality of sub regions divided in each lens
region like a Fresnel lens, the light shade is provided to
correspond to a region between lens regions where originally
exhibits crosstalk, achieving a reduction in cell gap without
deterioration in display grade.
Thirdly, the light shade may be switched on or off. For example,
the light shade may be switched off when it is desired to perform
display of a 2D image. In this case, even the light shade takes
parts in image display without a physically covered space. That is,
provision of a switchable black matrix may improve an aperture
ratio and brightness upon display of a 2D image.
It will be apparent to those skilled in the art that various
modifications and variations can be made in the present invention
without departing from the spirit or scope of the inventions. Thus,
it is intended that the present invention covers the modifications
and variations of this invention provided they come within the
scope of the appended claims and their equivalents.
* * * * *